Type I (restricted) and Type II (cross-reacting) tumor antigens of the transplantation rejection type (TATA), and of tumor antigens (TA) assayed by other in vivo and in vitro techniques and of the immune responses they evoke have received major emphasis. As a corollary to this study, the biologic properties In vitro and In vivo of alien histocompatibility (H-2) antigens and of variant antigens in several neoplasms are under study. Purification of TATAs is under investigation with the ultimate purpose of defining these membrane and cytosol antigens, after purification, in physicochemical, biologic, and molecular terms and of assessing their diagnostic and therapeutic potentials.